1. Field of the Invention
The present invention relates to a medical device. More specifically, the invention relates to a balloon catheter that has an elongated, detached guidewire shaft that may be torn away during catheter exchange.
2. Background of the Invention
Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. Radial expansion of the coronary artery occurs in several different dimensions, and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the lumen.
One or multiple dilations may be necessary to effectively dilate the artery. In many instances, successive dilations using a succession of balloon catheters with balloons of increasingly larger diameters may be required. In order to accomplish the multiple dilations, the original catheter must be removed and a second balloon catheter tracked to the lesion. When catheter exchange is desired, it is advantageous to leave the guidewire in place while the first catheter is removed in order to insert the second catheter without having to reestablish the path by inserting a new guidewire. To remove a balloon catheter while leaving the guidewire in place, there must be a portion of the guidewire extending out of the balloon catheter at the proximal end so that the guidewire can be held in place while the balloon catheter is removed.
Two types of catheters commonly used in angioplasty procedures are referred to as over-the-wire (OTW) catheters and rapid exchange (RX) catheters. A third type of catheter, referred to as a multi-exchange (MX) catheter, is discussed below. An OTW catheter's guidewire shaft runs the entire length of the catheter and is attached to, or enveloped within, an inflation shaft. Thus, the entire length of an OTW catheter is tracked over a guidewire during a PTCA procedure. A RX catheter, on the other hand, has a guidewire shaft that extends within only the distalmost portion of the catheter. Thus during a PTCA procedure only the distalmost portion of a rapid exchange catheter is tracked over a guidewire.
If a catheter exchange is required while using a standard OTW catheter, the user must add an extension onto the proximal end of the guidewire to maintain control of the guidewire, slide the catheter off of the extended guidewire, slide the new catheter onto the guidewire and track back into position. Multiple operators are required to hold the extended guidewire in place while the original catheter is changed out.
A RX catheter avoids the need for multiple operators when changing out the catheter and therefore is often referred to as a “single operator” catheter. With a rapid exchange catheter, the guidewire is outside the shaft of the catheter for all but the distalmost portion of the catheter. The guidewire can be held in place without an extension when the catheter is removed from the body. Once the original catheter is removed, a subsequent catheter may be threaded onto the in-place guidewire and tracked to the lesion. However, one problem associated with RX catheters is that the external portion of the guidewire may become tangled with the catheter shaft during use.
In addition, there are instances when the guidewire and not the catheter must be replaced. For example, the guidewire may become damaged during the procedure or it may be discovered during the procedure that a different shape, length, or size of guidewire is needed. An OTW catheter, with the guidewire lumen extending the entire length of the catheter, allows for simple guidewire exchange. With a RX catheter, the guidewire lumen does not extend the entire length of the catheter. Therefore, current RX catheter designs do not allow for simple guidewire exchange while the catheter remains in place. The guidewire, and most of the catheter, must be removed from the body in order to exchange guidewires. Essentially the procedure must then start anew because both the guidewire and the catheter must be retracked to the treatment site.
A balloon catheter capable of both simple guidewire exchange and catheter exchange without the use of an exchange guidewire is particularly advantageous. A catheter designed to eliminate the need for guidewire extensions or exchange guidewires is disclosed in U.S. Pat. No. 4,988,356 to Crittenden et al., incorporated in its entirety herein by reference. This MX catheter includes a catheter shaft having a cut that extends longitudinally between the proximal end and the distal end of the catheter and that extends radially from the catheter shaft outer surface to the guidewire lumen. A guide member through which the shaft is slidably moveable functions to open the cut such that the guidewire may extend transversely into or out of the guidewire lumen at any location along its length. By moving the shaft with respect to the guide member, the effective over-the-wire length of the MX catheter is adjustable.
When using the MX catheter, the guidewire is maneuvered through the patient's vascular system such that the distal end of the guidewire is positioned across the treatment site. With the guide member positioned near the distal end of the catheter, the proximal end of the guidewire is threaded into the guidewire lumen opening at the distal end of the catheter and through the guide member such that the proximal end of the guidewire protrudes out the proximal end of the guide member. By securing the guide member and the proximal end of the guidewire in a fixed position, the catheter may then be transported over the guidewire by advancing the catheter toward the guide member. In doing so, as the catheter advances toward the guide member, the guidewire lumen envelops the guidewire and the catheter is advanced into the patient's vasculature. In a PTCA embodiment, the MX catheter may be advanced over the guidewire in this manner until the distal end of the catheter having the dilatation balloon is positioned within the stenosis and essentially the entire length of the guidewire is encompassed within the guidewire lumen.
Furthermore, the indwelling MX catheter maybe exchanged with another catheter by reversing the operation described above. To this end, the indwelling catheter may be removed by withdrawing the proximal end of the catheter from the patient while holding the proximal end of the guidewire and the guide member in a fixed position. When the catheter has been withdrawn to the point where the distal end of the cut has reached the guide member, the distal portion of the catheter over the guidewire is of a sufficiently short length that the catheter may be drawn over the proximal end of the guidewire without releasing control of the guidewire or disturbing its position within the patient. After the catheter has been removed, another catheter may be threaded onto the guidewire and advanced over the guidewire in the same manner described above with regard to the MX catheter. The MX catheter not only permits catheter exchange without the use of the very long exchange guidewire and without requiring withdrawal of the initially placed guidewire, but it also overcomes many of the other difficulties discussed in association with RX catheters.
It is among the general objects of the invention to provide an alternative catheter which allows for simple guidewire exchange and fluid delivery. Therefore, what is needed is a catheter design that overcomes the disadvantages set forth above. Specifically, what is needed is a catheter which allows for catheter and/or guidewire exchange without the use of an exchange guidewire, and which avoids the disadvantages associated with prior art catheter designs. Accordingly, there arises a need for an OTW catheter having a detached guidewire shaft which allows for catheter and/or guidewire exchange without the use of an exchange guidewire.